The present invention is related to a hydroisomerization process employing an improved catalytic composition. More particularly, this invention involves an isomerization process employing a catalyst composition comprising a hydrogenation function selected from the Group VIII metals, a hydrogen form crystalline aluminosilicate zeolite, and a refractory inorganic oxide.
The isomerization of alkylaromatics is well established in the art. This reaction is of considerable importance in the petroleum industry because of the substantially high value of certain alkylaromatics as starting materials in the production of polymers and polyester resins. Especially valuable is 2,6-dimethylnaphthalene (DMN) which is used in the production of polyesters. It has been the practice up until this time to isomerize alkylated aromatics to equilibrium mixtures of their isomers with a variety of catalysts. Friedel-Crafts catalysts, such as aluminum chloride, are known to be effective isomerization catalysts. Noble metals, such as platinum supported on halogenated alumina or silica alumina have also been used effectively to isomerize hydrocarbons. More recently, crystalline aluminosilicate zeolites which have shown catalytic activity have been effectively used in the isomerization of hydrocarbons. Both natural and synthetic crystalline aluminosilicates have been employed. Included among these are the Type X and Type Y zeolites as well as synthetic mordenite.
Specifically, the zeolites known as mordeniteshave received great attention. Mordenites are crystalline natural or synthetic zeolites of the aluminosilicate type: generally, they have a composition expressed in moles of oxide of EQU 1.0.+-.0.2Na.sub.2 O.Al.sub.2 O.sub.3.10.+-.0.5SiO.sub.2 ;
the quantity of SiO.sub.2 may also be larger. Instead of all or part of the sodium, other alkali metals and/or alkaline earth metals may be present.
In general, it is known that the sodium form of mordenite is not particularly effective for isomerization of hydrocarbons and that replacing all or, for the greater part, the sodium cations with hydrogen ions yields the more advantageous hydrogen form mordenite. Conversion of the sodium form to the hydrogen form can be accomplished by a number of means. One method is the direct replacement of sodium ions with hydrogen ions using an acidified aqueous solution where the process of ion exchange is employed. Another method involves substitution of the sodium ions with ammonium ions followed by decomposition of the ammonium form using a high temperature oxidative treatment.
The activity and selectivity of hydroisomerization catalysts depend on a variety of factors, such as the mode of catalyst preparation, the presence or absence of promoters, quality of raw materials, feedstock quality, process conditions, and the like. Suitable catalysts can be conventionally prepared by combining commercially available crystalline zeolites, such as, a hydrogen form mordenite, with a suitable matrix material followed by the addition of a Group Vill metal, and thereafter activating by conventional means. A new catalyst has been discovered which exhibits greatly improved isomerization performance when compared to conventionally prepared catalysts. It has been found to have particular use in a process to isomerize dimethylnaphthalene containing alkylaromatics preferably into 2,6-dimethylnaphthalenes.